Steven C. Switalski

E-Type Delayed Fluorescence of a Phosphine-Supported Cu2(μ-NAr2)2 Diamond Core: Harvesting Singlet and Triplet Excitons in OLEDs∥

A highly emissive bis(phosphine)diarylamido dinuclear copper(I) complex (quantum yield = 57%) was shown to exhibit E-type delayed fluorescence by variable temperature emission spectroscopy and photoluminescence decay measurement of doped vapor-deposited films. The lowest energy singlet and triplet excited states were assigned as charge transfer states on the basis of theoretical calculations and the small observed S(1)-T(1) energy gap. Vapor-deposited OLEDs doped with the complex in the emissive layer gave a maximum external quantum efficiency of 16.1%, demonstrating that triplet excitons can be harvested very efficiently through the delayed fluorescence channel. The function of the emissive dopant in OLEDs was further probed by several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current.

Oxygen Permeability of Sol-Gel Coatings

Sol-gel processes are applied to prepare organic-inorganic composite coatings. The purpose of this report is to evaluate the possibility of tuning the oxygen permeability of the resulting coatings. It is proposed that if the oxygen permeability is largely controlled by the hydrophobic character and the pore sizes of membranes, then the permeability of the solgel coatings could be tuned by adjusting the composition of the organosilane precursor. The oxygen permeability is measured by the selective oxygen quenching of phosphorescent probes, such as platinum octaethylporphine (PtOEP). The application of such sol-gel coatings for optical fiber oxygen sensors will also be discussed.

Near-infrared diffuse reflectance fiber optic spectroscopy for process monitoring applications

We have used fiber optic remote process to monitor processes at Kodak in the lab, in development or pilot, and in production. This talk will examine the use of near IR (NIR) diffuse reflectance spectroscopy as a process technology. Diffuse reflectance spectroscopy offers the capability of looking at powders, slurries, emulsions, and dispersions. Unlike attenuated total internal reflectance spectroscopy, diffuse reflectance offers the capability of interrogating both the liquid and solid phases of the material. This provides the ability to examine the physical state of the solid, such as particle size and morphology, even in a slurry, or in the presence of large amounts of solvent, in addition to the chemical quality of the solution. The use of the NIR spectral region provides the advantages of high signal-to-noise ratio, impressive photometric stability, and commercially available instrumentation, probes and optical fiber cable. Some representative examples will be presented to demonstrate the capabilities of diffuse reflectance spectroscopy for process monitoring with fiber optics.

Patterning Microparticles on a Template of Aggregated Cationic Dye

Patternwise aggregation of charged molecules on a surface is potentially a facile approach to generate a template on which to pattern oppositely charged microparticles. We report on the patterning of silica microparticles by a system comprising a photopatternable copolymer and an aggregate forming penta-cationic cyanine dye. A thin film of the copolymer, composed of a molar excess of styrenesulfonic acid oxime ester to cross-linkable glycidyl methacrylate monomomers, was exposed through a mask and neutralized, resulting in a pattern of hydrophobic areas, and where exposed, a hydrophilic cross-linked film with sodium poly(styrenesulfonate) domains. The occurrence and locus of aggregation of an aqueous solution of the dye, applied to the patterned surface was established by absorbance and fluorescence spectroscopy and atomic force microscopy. In exposed areas, dye is imbibed and aggregation induced in sodium styrenesulfonate domains internal to the layer, whereas in the unexposed areas the dye aggregates on the hydrophobic surface. Aqueous anionic silica microparticles applied to the dye treated patterned surface and then rinsed, are retained in the unexposed areas having cationic surface aggregates, but rejected from the exposed areas with internal dye aggregates as these areas retain net negative charge. Mask exposure, absent dye treatment, did not result in patterning as negatively charged microparticles were nowhere retained, and positively charged particles were everywhere retained. The extent of surface coverage by the dye in unexposed areas was deposition time dependent, and ranged from isolated patches covering about 20 percent of the polymer surface to a surface saturated layer, with silica particle patterning robust over the range of dye surface coverages studied. The force requirements to pattern the denser than water silica microparticles are identified, and particle and polymer film surface potentials that meet the critical repulsion force requirement are mapped using an established sphere-to-flat surface electric double layer (EDL) model.